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ISX

Speed/RPM calc..

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ISX

Spent a while making this thought you guys could have some fun with it too. You have to have microsoft excel for this file to work. Should work with any version.Don't mess with anything but the highlighted blue things or you might erase my formulas. If you do manage to delete it all and make it go nuts, just delete it and redownload the one here..

Speed-RPM 2.xls

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guesswho512

good work....really easy to use...thanksbut what is "Tire Thickness percentage (Required)" and how does that play a role?

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ISX

good work....really easy to use...thanks but what is "Tire Thickness percentage (Required)" and how does that play a role?

The middle of the tire formula (245/75/16) is a percentage... The 245 is the width of the tire in mm's. The 75 tells you how much of the width of the tire the sidewall height contains. As in, from the edge of the wheel to the outer part of the tire, is 75% of 245. Obviously this is America and we need English units so you convert 183.75 (75% of 245) into inches by multiplying that by 0.0393700787, now you have about 7.23", so if you measured the sidewall on that tire (the stock size) it would measure almost 7 1/4". So to get tire height you multiply 7.23 by 2 (since there are 2 sidewalls in tire height) and then add the wheel size of 16". Now you have a 30.5" tire.. Let me know if you don't understand that. Alright I updated the file it to make that part a little clearer.

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